There is a close relationship between tides or tidal currents and an amount of fish catch in a fishery. Particularly, in angling, fish schools can be effectively detected and caught by paying attention to a tide or a tidal current to find a good fishery. Since an amount of fish catch depends on a tide or a tidal current in an angling area, it becomes very important in fishing to obtain tide or tidal current data in an expected area and at a day and hour beforehand and to take into account the tide or the tidal current at an area when fish schools are detected.
When a ship proceeds through a strait or the like, tides or tidal currents may become obstructions, or they may help a ship to advance efficiently. Thus, it is important to know beforehand tides or tidal currents along a route the ship proceeds or to know a tide or a tidal current at the present position of the ship.
Conventionally, such tide or tidal current data have been edited by, for example, the Maritime Safety Agency to produce tides or tidal currents table. Thus, it has been possible to know tide or tidal current conditions corresponding to ages of the moon at various points in Japan.
However, the tides and tidal currents table is voluminous, since there are described therein tides or tidal currents data corresponding to ages of the moon at many points throughout Japan. It has taken much energy and a long time to search the relevant tide or tidal current at a desired place and a desired day and hour out of the data in the table.